The invention relates to anti-reflection materials advantageously used for display such as liquid crystal displays (LCD), plasma displays (PDP), CRT, EL and the like, specifically relates to anti-reflection materials having superior stain resistance on image displaying surfaces, anti-reflection property, chemical resistance and wear resistance. The invention also relates to a method for producing anti-reflection materials and polarizing film.
Displays typified by LCD, PDP, CRT and EL are widely used in various fields such as television and computer technologies, and have been rapidly developed. At the beginning of the development of displays, obtaining color images was a keyword for the development. Recently however, high vision color images has been one of keywords in the development of displays, so that more weight has been put on higher refinement and higher quality for images, and low electric power consumption. Displays supporting man-machine interface will be further widely used according to beginning of multimedia community. Especially, popularization of pocket telephones, PHS and other portable terminals will remarkably enlarges application of the above displays.
As displays for portable terminals, it is noted that liquid crystal displays, that are light, compact and suitable for wide use, may monopolize the market. Portable terminals containing touch-panel to which a plastic pen or a finger is directly contacts for operation have been widely used. Therefore, requirements for wear resistance, chemical resistance and stain resistance have become stricter than ever. Furthermore, requirements for anti-reflection, namely, preventing the outside lights such as sun light, fluorescent lamp, and the like from reflecting on a display when the display is used in the light such as outdoors has become stricter than ever. These requirements extend over not only portable terminals but also various types of displays from small sizes to large sizes.
With regard to materials for substrates used in anti-reflection materials, triacetyl cellulose (hereinafter referred to TAC) is usually used since that exhibits low in cost and excellent optical properties. However, TAC is very inferior in adhesiveness with water-type adhesive when TAC is laminated with a polarization substrate. In order to over come the above defect, they have been improved adhesiveness between a TAC film and a polarization substrate layer by saponifying the TAC film after forming a surface-roughened layer thereon. However, such treatment changes optical properties of the surface-roughened layer such as HAZE value thereof and the like, thereby resulting in defect of image contrast and image unevenness, so that clear images can not formed. In addition, hardness and wear resistance of the surface-roughened layer decrease, so that hardness of a surface layer which is formed on the surface-roughened layer decrease, thereby decreasing wear resistance of the anti-reflection material. Alternatively, in the case that saponifying to TAC film is conducted after forming a surface layer on a surface-roughened layer, the surface layer is easily solved by alkaline, thereby resulting in the same problems as mentioned above. Therefore, improvements of surface-roughened layer free from the above problems are desired.
On the contrary, in the case that a surface-roughened layer is formed on a saponified TAC film which is saponified, adhesiveness between the saponified TAC film and the surface-roughened layer is too inferior for critical use, and hence, improvements of surface-roughened layer is a essential subject. Therefore, it has been desired to provide laminate structures consisting of polarization substrate, transparent substrate and surface-roughened layer, having excellent optical properties and wear resistance without the above-mentioned problems. The objective of the invention is to solve the above-mentioned problems and provide anti-reflection materials having excellent optical properties and good adhesiveness with transparent substrates and superior durableness.
With regard to anti-reflection, it has been generally applied to disperse or diffuse the light so as to graduate the image such as ground glass. In order to disperse or diffuse the light, an incidence surface of the light is essentially roughened. For surface roughening treatment, sandblast, embossing and the like that directly roughen a surface have been applied. Alternatively, it has been applied to provide a coating layer including a filler, or a porous layer on a surface of a substrate.
In the method providing a coating layer including a filler, the roughness of a surface-roughened layer can be easily controlled by selecting the particle size of the filler and the producing process thereof is simple, so that the method is preferably used. The resin used for the coating materials is preferably improved in transparency, heat resistance, wear resistance, chemical resistance and the like. As substrates are formed by plastic film that are high in transparency and low in heat resistance, UV-curing resins are preferably used. For example, Japanese Patent Unexamined Publication (Kokai) No. 1 (89)-105738 and No. 5(94)-162261 disclose structures including an UV-curing resin and a silica pigment.
However, silica pigment is high in oil absorptiveness, so that oil such as fingerprints is easily absorbed in the pigment in a surface roughened layer and the surface thereof is easily stained. Additionally, the stain can not be easily wiped off by using a cloth soaked with a solvent such as alcohol. Furthermore, the silica pigment sharply projects from the surface-roughened layer, so that fibers of the cloth cling to the ends of the silica pigment. As a result, the surface of the display becomes white, thereby deteriorating the image contrast thereof.
As another method for anti-reflection, it is noted that by alternatively coating a material with a high index of refraction and a material with a low index refraction (multi-coating), reflection on a surface can be restricted. The multi-coating layer is generally formed by sol-gel method or gaseous phase method which is alternatively coating a material with a low index of refraction typified by SiO.sub.2 and a material with a high index of refraction such as TiO2, ZrO.sub.2 or the like by means of deposition. It is proposed to form such multi-coating on the surface-roughened layer. However, such structure maintains the above mentioned problem that stain can not easily be wiped off. The reason is that the silica pigments sharply project from the surface-roughened layer, so that the shape of the surface layer of the multi-coating profiles the sharpened projection, whereby the roughness of the surface layer becomes sharp. As a result, the multi-coating maintains the above mentioned problem, and a part of the silica particles penetrate the surface layer, thereby easily absorbing oil such as fingerprints.
In addition, the gaseous phase method is not suitable for treatment for large area and high in apparatus expense. The sol-gel method is high in factory consumption since coating and baking must be repeated. Furthermore, the multi-coating formed by the sol-gel method is colored to violet or green type color, thereby showing the stain more remarkably than the surface-roughened layer without multi-coating. In order to prevent from staining, it is proposed to coat a flourine-type material on the surface-roughened layer. This proposal however can not solve the problem since the affect of the surface-roughened layer is still included.
According to higher resolution of displays, fineness of the height and the pitch of the roughness in the surface-roughened layer has been required. The higher refinement of images owes to higher density of dots of images. When the pitch of the roughness is larger than the pitch of the dots, glittering occurs due to interference. Therefore, in order to form clear images without reflection and glittering, it is critical to control the height and the pitch of the roughness in a restricted range without unevenness.
However, dispersion property of the surface roughed layer consisting of an UV-curing resin and a silica pigment is not sufficient. In addition, the surface-roughened layer before UV curing is liquid with low adhesive, so that the particles of the silica pigment adhere each other in the meantime from coating a coating material on a substrate to UV radiation, whereby coagulation (orange peel) is formed on the surface of the surface-roughened layer. Especially, coagulation becomes remarkable when the contain of silica pigment increases or the coating material for the surface-roughened layer is diluted by a solvent for controlling of the thickness thereof.
Therefore, another objective of the invention is to provide an anti-reflection material which exhibits excellent anti-reflection properties by means of preventing the outside lights such as sun light, fluorescent lamp, and the like from reflecting on a display, which gives clear images without glittering and reduction of image contrast, and, which exhibits excellent wear resistance, chemical resistance, optical stability and stain resistance. The objective of the invention is to provide a polarizing film manufactured by the above anti-reflection material, whereby remarkably improve properties of full color liquid crystal displays and the like.